Concentration and separation of granular mixtures



y 7, 1953 H. B. CANNON ETAL 2,644,583

CONCENTRATION AND SEPARATION OF GRANULAR MIXTURES Filed July 5, 1949INVENTOFS: HARRYB. a4NN0N 10 OSCAR H. TR UDEAU Tiff/[ATTORNEYS PatentedJuly 7, 1953 UNITED STATE GONCENTRATION AND SEPARATION OF GRANULARMIXTURES Application July 5, 1949, Serial No. 103,048

2 Claims.

Our invention relates to a method and apparatus for concentrating andseparating mixtures of granular materials. More particularly it isconcerned with the separation of ores contained in aqueous slurries intoseveral portions one of which contains most of the minerals of value,while another contains so little that it may economically be discarded.

It is frequently desirable, if not essential, to concentrate the ore atthe mine face and to discard the bulk of uneconomic material therein,before transporting the concentrated minerals to a location where thedesired constituents can be recovered and refined. In many miningoperations the ores are of such low grade that an economic recovery ofdesired constituents would otherwise not be possible.

A classic example of such an operation is the placer mining of gold andtin by means of dredges. It is essential therein that the great bull: ofthe worthless quartz sands be separated from their valuable mineralcontents at the dredging site, thus greatly reducing the amount ofmaterial to be transported and subjected to subsequent processing. Forthis purpose various types of shaking tables, stationary tables, jigs,troughs, sluices and the like have been suggested. One of the mostsuccessful in recent years is the sO-called Humphreys Spiral. Thisconsists of a chute in the form of a helix in which separation isperformed by stratification of the material during its travel down thechute, the various fractions being drawn off through separate openingsalong the path of travel. This equipment is, however, quite heavy andbulky.

It is an object of our invention to improve the concentration andseparation of granular mix tures. A further object is to provide amethod and apparatus whereby such concentration of desired minerals maybe effected cheaply at the mining site. Another object is to provideequipment for this purpose, that is readily portable, occupies a minimumamount of space and yet possesses a large capacity and high efficiency.Additional objects and advantages will become apparent as thedescription of our invention proceeds.

Broadly speaking, our invention involves the use of an inclined troughor sluice having converging sides and a relatively narrow outlet, overwhich the granular mixture, preferably in the form of an aqueous slurry,flows and where it becomes stratified. Combined therewith are meanslocated in the zone of free fall beyond said outlet, whereby theeffluent fan is divided into several portions containing widely varyingconcentrations of the constituents of the mixture.

The inclined trough employed according to our invention may have theform of a triangle with the narrow outlet at the apex and be providedwith vertical sides, preferably of increasing height as the outlet isapproached, to contain the material being processed. This form may aptlybe described as a pinched sluice. If the angle at the apex is keptsmall, the supporting surface, i. e., the bottom of the trough, may beflat. As this angle is increased, there is an increasing tendency forthe granular material to build up in depth along the sides, therebycreating high velocity and turbulence which tendency be largely overcomeby providing the pinched sluice with a rounded bottom.

It will be apparent that upon increasing the angle at the apex of flowto 360, one will arrive at an inverted cone with a circular outlet atits apex. This constitutes a preferred embodiment of our invention,because it provides maximum capacity with minimum space and weight ofequipment. It will be noted that the cone-shaped inclined convergingtrough has the rounded supthe outlet, and that the separation intoportions of widely varying compositions can most effectively take placethere. Any attempt to introduce the dividing means through the outletand above the floor of the trough results in a piling up of the densestportion of the material treated and consequent loss of efiiciency oreven complete failure of the device.

The dividing means employed according to our invention is preferablyformed by the edge of a metal sheet or the like, that is disposed in aplane of stratification at right angles to the direction of flow.Preferably this splitter is adjustable at right angles to the planes ofstratification, in order to permit processing of various materials andto achieve optimum benefication of each.

In many cases, we employ two such splitters, thus dividing the effluentfan into three distinct portions. For the sake of convenience the por-'tion containing most of the desired constituents will be termed theconcentrate. The intermediate portion that is usually reprocessed willbe termed the middlings, while the portion having the lowest values,that is usually discarded, will be called the tails. Obviously, it ispossible within the scope of our invention to employ but a singlesplitter or more than two, depending upon the number of distinctfractions desired.

In a preferred embodiment of our'invention a special rounded lip orguide plate is provided at the bottom edge of the narrow trough outlet,forming a downwardly curved extension of the trough bottom, whereby theefiluent fan is spread due to surface attraction. The spreading of thefan and the further slowing up of the densest fraction thereby attained,renders thesubse uent splitting into distinct fractions more effective.

Our method and apparatus are applicable to any well divided ore that maybe caused to flow as such or suspended in a liquid over the inclinedconverging trough. It is particularly applicable to mineral bearingsands found in nature, such as sands containing ilmenite, rutile,

zircon, cassiterite, pebble phosphate or like minerals. It may also beapplied to ores that have previously been ground finely enough to freethe minerals of value from the gangue materials, and to permit them tobe flowed as such or as suspensions in a liquid medium.

While the concentration and separation of ores is probably the mostimportant application of our invention, the method and apparatus mayalso be applied to the concentration and separacause stratification. Forexample, mixtures of seeds, grains and of various manufactured granuiarmaterials may be treated by our method in tour apparatus.

In most cases of ore concentration, we prefer to treat an aqueous slurrycontaining a high percentage ofore, for example, one having a solidscontent of between about and about 65%. If desired, flotation reagentsmay be added to the slurry in order to influence stratification of thevarious solid constituents. In such case the topmost portion of the fanusually constitutes the concentrate. The freshly-formed slurry is fedevenly to the wide upper end of the inclined converging trough, and thesplitters beyond the narrow outlet are adjusted for optimum separationof the particular material processed. When using two splitters, weprefer to reprocess the middlings and sometimes also the tails. Ifdesired, the concentrate may likewise be reprocessed to eliminateadditional waste material before being transported to the refinery.

To facilitate a full comprehension of our in vention and to illustratehow it may be carried out in practice, reference will now be made to theaccompanying drawings in which Fig. 1 shows a simplified plan view of aninclined converging table and single splitter according to oneembodiment of our invention, and

Fig. 2 shows a side view of the device of Fig. 1, including also thefeeding and collecting means.

Fig. 3 is a simplified vertical cross section of the cone-shapedembodiment with two splitters, including feeding and collecting means.

Referring now to the device shown in Figs. 1 and 2, i represents theinclined triangular supporting surface (bottom of the trough) and 2 thenarrow outlet at its apex. 3 are the vertical sides of increasing heightas the outlet is approached. 4 is a vertical back to prevent spilling ofthe material as it is fed to the wide upper end.

A feeding box 5 with baffles I4 is indicated in Fig. 2. It serves todistribute the material evenly along the wide upper end, whence itbegins to flow down the inclined converging surface. A rounded lip orguide plate 6 is shown at the bottom edge of the outlet. This can bedispensed with, but generally improves the separation of the fan. 7

Beyond and below the outlet 2 are the dividing and collecting means.These consist of the splitter l, which is preferably bent near the top,as shown in Fig. 2, so that its upper edge will cause a minimum ofturbulence at the point of separation. On either side of the splitterare catch basins 8 and 9, separated thereby, in which the two distinctportions of the flow are collected and from which they are withdrawnthrough the separate outlets it and H.

The splitter I may be adjusted vertically in the path of flow by raisingor lowering it. This is accomplished, as can best be seen from Fig. 2,by means of the gears 52 and ratchets l3. Obviously, raising andlowering the splitter "l in this manner will vary the portions of theflow divided thereby.

The pinched sluice shown in Figs. 1 and 2 is provided with a flat bottomI for simplicity of construction. If the angle at its apex is materiallyincreased, it is advisable to substitute a rounded bottom, in order tominimize high velocity and turbulence along the vertical sides 3 and theadjacent bottom. The dimensions of the sluice may be Varied widely andthe optimum dimensions will depend largely upon the type of material tobe processed. The same is true of the degree of inclination. Whentreating i1- menite bearing sands containing approximately 2% ofilmenite, we-have obtained excellent results by employing sluices about3 to 4 feet long, 12 to 14 inches Wide at the upper endand having anoutlet at the lower end from to 2 inches wide. In the case of thenarrower outlets, the preferred inclination of the trough bottom I wasabout 17 to 18, while for the wider outlets a 'lesser inclination ofabout 13 to 16 gave best results. The narrower outlets favored a sharperseparation in relation to the specific gravities of the individualgrains, whereas the wider outlets permitted the treatment of much largerquantities with a sharper separation in relation to the grain sizes. Thespecific figures given are obviously merely for purposes ofillustration,

since the optimum proportions of the pinched sluice will depend upon thetype of material processed.

Turning now to Fig. 3, 3! represents the inverted cone that forms theinclined converging trough. 32 is the narrow outlet at the apex of saidcone. At the upper end of the cone 3| an upright edge portion 33 isprovided to prevent splashing over of the materials fed. Disposed abovethe inverted cone 3| and fitting within its upright edge 33 is anupright feeding cone 34. This acts to distribute the materials fedthrough the feeding line 35 evenly to the outer and upper edge of theinverted cone 3 I.

The lower edge of the inverted cone 3|, that forms the narrow outlet 32has a rounded lip 35 to aid in spreading the fan. Within the outlet 32and a zone free fall of the efiluent material are two concentric tubularsplitters 3'! and 3B. The upper edges of these splitters are preferablyflared outwardly to minimize turbulence. splitters are adjustablevertically by means of gears 39 and ratchets 40, as in the case of theembodiment shown in Figs. 1 and 2.

A catch basin 4| with an outlet 42 is provided to collect and carry offthe densest fraction of the material passing through the outlet 32.Another catch basin 43 and outlet 44 are provided for the intermediatefraction, while the tube that forms the splitter 38 serves to carry offthe lightest fraction. Here again it is apparent that the relative widthof the outlet 32 and the inclination of the inverted cone side will bevaried depending upon the material processed.

The operation of our ore concentrators is believed to be evident fromwhat has been said above. A few moredetails will be given to assist in athorough understanding of the practice of our invention.

It is possible to feed a readily flowable, dry material, in which casesome means of imparting vibration to the inclined converging trough maybe provided. We have obtained best results when employing a, ratherconcentrated aqueous slurry. The feed must be distributed evenly alongthe upper, wide edge of the trough, so that it will flow to the narrowoutlet with a minimum of turbulence. The narrowing of the width of flowas the outlet is approached, greatly assists in bringing about afar-reaching separation and thorough stratification of the variousconstituents, thereby increasing the efficiency of the dividing meansth-atare inserted into the fan beyond the outlet.

It is essential for the efliciency of our concentrator that thesedividing means be located in a zone of free fall of effluent materials.Best results are obtained when the upper edge of the dividing means islocated just beyond the supporting surface of the trough. The splittershould, furthermore, cut sharply across the entire width of the fan. Byobserving these precautions detrimental turbulence and undue impedanceor stoppage of the flow can be avoided.

In most cases our separators can be used most efficiently in groups, oneabove the other, so that the fractions separated in one group canimmediately be reprocessed, after suitable combination, in a groupbelow. The great saving in space and weight achieved by our devices,becomes most evident when they are employed in groups. For example, itbecomes possible to mount a number of them on a barge floated behind adredge and to thus provide adequate capacity for all material raised bythe dredge.

Extensive tests of our pinched sluice embodi ment employing ilmenitesands containing about 4% of heavy minerals, have demonstrated that wecan consistently obtain a concentrated product containing about 85% ofheavy minerals with The v a loss of only about 15% of the total heavyminerals present in the original sands. This can be accomplished at ahigh rate of throughput employing three to four stages, i. e., severalcountercurrent reprocessings, with a relatively small investment forequipment and in relatively little spacing, as compared with otherconcentrating devices now being employed.

It will be obvious that the details of our method and apparatus aresubject to considerable variation without departing from the spirit andscope of our invention. Some of the variations have been referred to inthe foregoing'and others will be evident to those skilled ,in the art.All such variations are included within the scope of the appendedclaims, unless expressly excluded by limitiations set forth therein.

We claim:

1. A separator of granular mixtures, which comprises an inverted conehaving a circular outlet at its apex, means for evenly feedingafiowablematerial to the upper edge of said cone, and dividing means locatedwithin said outlet in the normal path of flow from said cone, saiddividing means including a substantially tubular member whose upper edgeis disposed horizontally across the path of flow in a zone of free falland spaced from the periphery of the said apex.

2. A separator of granular mixtures, which comprises an inclined, flowconverging portion having the configuration of an inverted frustrum of acone, said portion terminating in a centrally located discharge opening,and dividing means located within said discharge opening in the normalpath of flow from said portion, said dividing means including asubstantially tubular member whose upper edge is disposed horizontallyacross said path of flow in a zone of free fall and. spaced from theperiphery of the discharge opening.

HARRY B. CANNON. OSCAR H. TRUDEAU.

References Cited in the file of this patent UNITED STATES PATENTS NumberFOREIGN PATENTS Number Country Date France Mar. 17, 1918 Drelon Dec. 18,1951 Great Britain Oct. 1.8, 1948

